The present invention relates to a process of manufacturing hollow jewelry.
There are many well known processes used in the large volume production of jewelry. Such processes include die striking, casting and electroforming, all of which are used for producing metallic jewelry articles. Such production methods are capable of facilitating high volume, high speed production with very good reproducibility.
Jewelry articles are most commonly manufactured by investment casting. The process comprises of first creating a first model in exact detail out of sculpting wax. This is generally carried out by creating flexible rubber mould of the required design and then injecting a fluid wax to create the original piece. The wax pieces are then attached to a wax pole or sprue to form a wax tree. The said wax tree is then encased in plaster and allowed to cure and dry. After the chunk of plaster has been allowed to dry it is then placed in a hot kiln so the wax piece inside of it can melt and burn out. A hollow void is left in its place, which replicates the wax tree in complete detail. The chunk of plaster with the hollow shape of the wax tree is then it is placed in a centrifugal jewelry casting device that will use centrifugal force to drive molten gold down through an opening in the chunk of plaster where it will fill the hollow spot left by the wax melting out. After it has cooled the plaster is broken open to reveal a piece of gold jewelry.
Since jewelry articles are most often formed of precious metals such as gold or silver, hollow jewelry article with low precious metal content are often desirable since they reduce the cost of the final product. Hollow jewelry articles are also light in weight and more acceptable particularly for earrings, necklaces etc.
One method of producing such hollow jewelry is by electroforming. The process comprises fabricating the metal part by depositing a layer of the desired metal over a base form or substrate which is subsequently removed. The substrate may be suitable removed by chemical treatment leaving only the thin metal layer behind. Examples of such processes have been described in U.S. Pat. Nos. 5,172,568 and 4,343,684. The main disadvantage with the technique is that it requires special equipment designed for electroforming. Electroforming also places design limitation on the article since it may be difficult to produce narrow recesses and sharp angles. Articles manufactured by this process also lack sufficient tensile strength to withstand any external stress.
Use of acid or water soluble wax inserts in mold cavities to mold partially or completely hollow articles is another method used for the reduction of production costs by reducing the amount of precious metal in the end product. Generally. the process comprises placing a soluble wax core insert in a mold cavity and injecting molten plastiwax into the cavity which surrounds the soluble core insert. The core insert is then removed by chemical treatment to produce a plastiwax mold having a hollow core. The said mold is then sent for investment casting to obtain the precious metal gold jewelry. A primary disadvantage of this process is that any accidental change alignment of the core insert or the shifting of the core insert in the mold can cause damage to the shape and size of the article. Attempts have been made to ensure no changes in the alignment take place. For ex. U.S. Pat. No. 5,606,873 discloses use of spacer pins to hold the mold in place and to maintain a prescribed clearance between the wax core insert and the mold cavity.
U.S. Pat. No. 6,554,052 provides a method or process for fabricating a hollow jewelry article which is hollowed or bored out to an arcuate extent of 200°.
There is a continuing need to develop a process for preparing hollow jewelry which is economical, simple and efficient for large volume production of hollow jewelry articles which posses sufficient tensile strength.
In view of the foregoing, it is an object of the present invention to provide an improved process for producing jewelry articles manufactured with a reduced amount of precious metal thereby decreasing the cost of producing jewelry articles capable of withstanding external stress.